Originally Posted by Slo86GT
Soooo if a 5.0L pushrod made 225hp from the factory with 2.25" dual pipes... Why does it gain power moving to a 2.5" system? I daresay that a 2.0L making 160hp from the factory is moving much more air volume than that weezy 2.5L per bank engine.
I honestly don't give much credit to the backpressure theories on modern cars where multiple cats are retained. The cats are a blockage, and force backpressure to be retained for the engine side of things, cancelling out most if not all pulsation in the exhaust flow, and anything post-cat system is made better by open pipes.
Pv=nRT, which is the ideal gas law will explain the principle of how the exhaust gasses flow at a very basic level.
The stock system on the 5.0 L was quite restrictive at the time.
Modern catylasts don't pose nearly the restriction on flow or increase in back pressure as the earlier systems did as well.
Only the PZEV models have two catalysts though for the 2012+ 2.0 L GDI Ti-VCT, the regular models only have the integrated exhaust manifold catalyst.